Photosynthate Distribution Research Articles

Interaction between sieve element and companion cell and the consequences for photoassimilate distribution. Two structural hardware frames with associated physiological software packages in dicotyledons?

The unique properties of the sieve element/companion cell complex (SE/CC complex) are based on the concerted action of SE and CC. A prominent role in this interaction is played by the branched plasmodesmata (pore-plasmodesma units, PPUs) between SE and CC. The large molecular exclusion limit of the PPUs enables an intensive exchange of macromolecular materials and messengers. Further, the degree of symplasmic autonomy of the SE/CC complex and the structural/functional properties of the SE/CC modules may differ between the dicotyledonous families. The speculation is advanced that the difference in building blocks produces two distinct phloem frames ('hardware') with associated physiological programmes ('software'). The implications of two phloem types for photosynthate distribution and relative growth rate are discussed.

Effect of Vesicular-Arbuscular Mycorrhizal Fungi on the Growth, Photosynthesis, Transpiration and the Distribution of Photosynthates of Bearing Satsuma Mandarin Trees.

The response of satsuma mandarin (Citrus unshiu Marc. cv. Okitsu wase) on trifoliate orange (Poncirus trifoliata Raf.) rootstocks to inoculation of vesicular-arbuscular mycorrhizal (VAM) fungi, such as Glomus ambisporum Smith and Schenck, Gloumus fasciculatum (Thaxter) Gerdemann and Trappe emend. Walker and Koske, Glontus mosseae (Nicolson and Gerdemann) Gerdemann and Trappe, and Gigaspora ramisporophara Spain was studied at low phosphorus (P) application.Under high air temperature stress conditions in August, the photosynthetic (Pn) and transpiration (Tr) rates of VAM-inoculated trees were faster than non VAM ones. But in September when air temperature decreased, the Pn and Tr rates did not differ significantly between VAM-inoculated trees and non infected ones. In general, infected trees had larger leaf area and higher leaf P concentration and the tree growth was more vigorous than was that of non infected ones.When 13CO2 was fed to fruit-bearing trees under the optimal air temperature conditions, fruits were the strongest sink for photosynthates and new leaves were the second strongest. The leaves of VAM and non VAM trees assimilated 13CO2 equally fast per unit leaf area, and the distribution of 13C into various parts of the bearing trees did not differ. VAM trees, however, had 3 times more photoassimilates per tree than uninfected ones because the former had a leaf area 3 times larger than the latter and grew more vigorously.

Short-term control of root: shoot partitioning

We present data showing that the fraction of the available photosynthate partitioned between the root and the shoot of a barley seedling is affected by the supply of photosynthate from the source leaf: an increased fraction of the exported photosynthate goes to the shoot when supply is reduced. Also, if the roots are cooled a short time before reducing the supply of photosynthate, then the effect of a reduced supply upon partitioning is reversed with an increased fraction then going to the root. We conclude that the distribution of available photosynthate between competing sinks is influenced by source supply as well as sink function

Soil Sheaths, Photosynthate Distribution to Roots, and Rhizosphere Water Relations for Opuntia ficus-indica

Soil sheaths incorporating aggregated soil particles surround young roots of many species, but the effects of such sheaths on water movement between roots and the soil are largely unknown. The quantity and location of root exudates associated with soil sheath formation and root water loss were therefore examined for Opuntia ficus-indica, which has prominent soil sheaths along the entire length of its young roots, except within 1.4 cm of the tip. The soil sheaths, which averaged 0.7 mm in thickness, were composed of soil particles and root hairs, both of which were covered with exuded mucilaginous material. As determined with a ¹⁴C pulse-labeling technique, 2% of newly fixed ¹⁴C-photosynthate was translocated into the roots at 3 d, 6% at 9 d, and 8% at 15 d after labeling. The fraction of insoluble ¹⁴C in the roots increased twofold from 3 d to 15 d. Over the same time period, 6%-9% of the ¹⁴C translocated to the roots was exuded into the soil. The soluble ¹⁴C compounds exuded into the soil were greater in the 3-cm segment at the root tip than elsewhere along the root, whereas mucilage was exuded relatively uniformly along roots 15 cm in length. The volumetric efflux of water increased for both sheathed and unsheathed roots as the soil water potential decreased from -0.1 MPa to -1.0 MPa. The efflux rate was greater for unsheathed roots than for sheathed roots, which were more turgid and had a higher water potential, especially at lower soil water potentials. During drying, soil particles in the sheaths aggregate more tightly, making the sheaths less permeable to water and possibly creating air gaps. The soil sheaths of O. ficus-indica thus reduce water loss from the roots to a drying soil.

Spatial Distribution of Photosynthesis during Drought in Field-Grown and Acclimated and Nonacclimated Growth Chamber-Grown Cotton

Inhomogeneous photosynthetic activity has been reported to occur in drought-stressed leaves. In addition, it has been suggested that these water stress-induced nonuniformities in photosynthesis are caused by "patchy" stomatal closure and that the phenomenon may have created the illusion of a nonstomatal component to the inhibition of photosynthesis. Because these earlier studies were performed with nonacclimated growth chamber-grown plants, we sought to determine whether such "patches" existed in drought-treated, field-grown plants or in chamber-grown plants that had been acclimated to low leaf water potentials (psi(leaf)). Cotton (Gossypium hirsutum L.) was grown in the field and subjected to drought by withholding irrigation and rain from 24 d after planting. The distribution of photosynthesis, which may reflect the stomatal aperture distribution in a heterobaric species such as cotton, was assayed by autoradiography after briefly exposing attached leaves of field-grown plants to (14)CO(2). A homogeneous distribution of radioactive photosynthate was evident even at the lowest psi(leaf) of -1.34 MPa. "Patchiness" could, however, be induced by uprooting the plant and allowing the shoot to air dry for 6 to 8 min. In parallel studies, growth chamber-grown plants were acclimated to drought by withholding irrigation for three 5-d drought cycles interspersed with irrigation. This drought acclimation lowered the psi(leaf) value at which control rates of photosynthesis could be sustained by approximately 0.7 MPa and was accompanied by a similar decline in the psi(leaf) at which patchiness first appeared. Photosynthetic inhomogeneities in chamber-grown plants that were visible during moderate water stress and ambient levels of CO(2) could be largely removed with elevated CO(2) levels (3000 muL L(-1)), suggesting that they were stomatal in nature. However, advanced dehydration (less than approximately 2.0 MPa) resulted in "patches" that could not be so removed and were probably caused by nonstomatal factors. The demonstration that patches do not exist in drought-treated, field-grown cotton and that the presence of patches in chamber-grown plants can be altered by treatments that cause an acclimation of photosynthesis leads us to conclude that spatial heterogeneities in photosynthesis probably do not occur frequently under natural drought conditions.

Biochemical composition and photosynthate distribution in sea ice microalgae of McMurdo Sound, Antarctica: evidence for nutrient stress during the spring bloom

The nutrient status of microalgae inhabiting sea ice in McMurdo Sound, Antarctica was evaluated during the peak and decline of the spring bloom in November and December. Natural populations of microalgae were analysed for C, N, chlorophyll a, protein, lipid, polysaccharide, and low-molecular-weight carbohydrate content, and for the distribution of 14C-labelled photosynthate into macromolecular fractions. Ratios of N:C and protein to carbohydrate (PR:CHO) were similar to values reported for nutrient-limited phytoplankton. Biochemical ratios and 14C-photosynthate allocation patterns suggest that microalgae from congelation ice habitats may be more nutrient-stressed than those from underlying platelet ice habitats. This trend would be consistent with the presumed gradient of seawater nutrient influx through the platelet layer to the bottom congelation ice habitat. Microalgae from congelation ice subjected to an experimental depletion of nutrients (particularly nitrate) showed decreased N:C, PR:CHO, and allocation of 14C-photosynthate to proteins. This evidence suggests that sea ice microalgae are nutrient-stressed during the peak and decline of the spring bloom in McMurdo Sound, which presumably begins when microalgal biomass concentrations and demands for growth reach or exceed the rate of nutrient supply from underlying seawater.

Distribution of (14)C-labeled photosynthate in loblolly pine (Pinus taeda) seedlings as affected by season and time after exposure.

Distribution of (14)C-labeled photosynthate was determined in field-grown loblolly pine (Pinus taeda L.) seedlings on August 9 and October 15, 1984 and January 15 and March 12, 1985. Leaves on a lateral branch fixed (14)C photosynthetically and amounts of (14)C in seven biochemical fractions in each of six plant parts were determined 8, 24, and 72 h later. In all treatments, (14)C uptake was approximately 96% of that originally presented. Respiratory loss of (14)C ranged from 22 to 87% of uptake and increased sharply with increasing time after exposure and as the seedlings grew larger later in the study. Most (14)C was found in exposed leaves and very little occurred above the exposed branch. Amounts of (14)C decreased in the exposed leaves and increased in the roots with time after exposure and date. Sugars were generally the most heavily labeled fraction. Labeled sugar content of exposed leaves decreased by more than half between 8 and 72 h as sugars were metabolized and translocated to other parts, primarily the roots. In roots, the labeling of starch and residue (structural compounds) increased greatly with transport time and season. In all plant parts, proteins and amino acids contained very little (14)C regardless of date or time.

Distribution and metabolism of current photosynthate by single-flush northern red oak seedlings.

Carbon distribution and metabolism by northern red oak seedlings (Quercus rubra L.) were followed for 72 h after a 30-min photosynthetic exposure to (14)CO(2). Approximately 50% of the assimilated carbon was lost during this time, presumably through respiration. Most of the (14)C recovered in the plant remained in the source leaf. Most of the exported (14)C was found in stems and especially roots. Position of the source leaf did not affect distribution of translocated (14)C; however, upper source leaves retained slightly more (14)C than lower source leaves. Most (14)C in all tissues was found initially in sugars. Labeled carbon in this fraction decreased rapidly and increased in other chemical fractions, particularly residue (structural carbohydrates and lignin). More (14)C was incorporated into residue than into any other chemical fraction, indicating continued growth by each of the tissues during the lag stage of seedling development. Labeled carbon increased in proteins for 6 to 12 h after treatment, then remained essentially constant for the remainder of the transport period, indicating both rapid incorporation of the pulsed (14)C into, and slow turnover of, the labeled protein components. In source leaves, (14)C incorporated into starch in the light was lost during the dark period, a typical diurnal storage pattern. In stems, (14)C in starch increased for 12 h, then decreased during the dark period, and then increased during the rest of the transport period. This pattern indicates that stems have both diurnal and long-term storage pools of starch. In roots, (14)C in starch increased rapidly for 12 h, then remained constant for the rest of the transport period, indicating primarily long-term storage in this tissue. Peak (14)C in amino acids in taproot preceded that in stem tissue, indicating recycling of (14)C from the roots to the shoot in amino acids.

Effect of simulated acidic fog on carbohydrate leaching, CO 2 assimilation and development of damage symptoms in young spruce trees ( Picea abies L. Karst)

The effect of acidic fog on carbohydrate leaching, CO 2 assimilation, carbohydrate status, and cuticle development of young spruce trees was studied in a greenhouse experiment. Over a period of 9 weeks the plants were subjected to fog application on 27 occasions. In one treatment trees were exposed to a fog of pH 2.75 (acidic fog) and in one treatment to a fog of pH 5.00 (control treatment). Leaching rates for carbohydrates (sucrose, glucose, fructose) were significantly higher in the acidic fog treatment than in the control treatment. The total amount of carbohydrates leached out of the trees by acidic fog, however, was low and amounted to less than 1% of the non-structural carbohydrates in the needles. Trees which had been exposed to acidic fog were not affected in photosynthesis and in the distribution of photosynthates to various plant parts. In the younger needles significantly lower concentrations of starch, glucose, and fructose were found in the treatment with acidic fog as compared with the control plants. Also the starch concentration in the roots of the control plants was significantly higher than that in the plants exposed to acidic fog. These findings are suggestive of a stress situation with a high energy demand. Application of acidic fog resulted in a disintegration of the epicuticular wax layer and of the epistomatal wax props. In the treatment with acidic fog some needles of the current year turned reddish-brown and some older needles became chlorotic and later brown. These needles were shed to a large degree. Needle loss of the trees exposed to acidic fog was significantly higher than that of the control trees.

Assimilation and Distribution of Photosynthate in Winter Wheat Cultivars Differing in Harvest Index

Yield differences among New York winter wheat (Triticum aestivum L.) are related to harvest index. This study was conducted to see how four cultivars, which differed in harvest index and plant height, differed in partitioning of photosynthate before and during grain filling. Experiments were conducted in field plots grown at Hamden, CT in 1985 and 1986 in Cheshire fine sandy loam (coarse‐loamy, mixed, mesic Typic Dystrochrept). The assimilation, distribution, and retention of radioactivity from 14CO2‐derived photosynthate was measured. In each year, the canopy was labeled at heading and early and late in grain filling. Harvest index was inversely related to stem height. The fractional distribution of the 14C remaining at maturity varied with labeling date and cultivar. The amount in the spike was 0.35 to 0.5 when labeled at heading, with less than 0.15 in the grain. When labeled during grain filling, a greater fraction of 14C was distributed to the spike in the semidwarf than in the tall cultivars, 0.9 and 0.8, respectively, and most of the 14C in the spike was in the grain. Almost half of the radioactivity initially assimilated was lost from the plants by maturity. Tall semi‐dwarf ‘Purcell’ retained a greater fraction of radioactivity initially assimilated than did tall ‘Honor’, 0.56 and 0.51, respectively. Thus, differences in harvest index were related to differences in distribution of photosynthate and to differences in retention of photosynthate to maturity.

イチゴの栄養生長期から休眠期にかけての光合成と光合成産物の転流•分配

Photosynthesis and translocation and distribution of photosynthates in ‘Donner’ strawberry plants were investigated, extending from the stage of vegetative growth to that of imposed dormancy.1. Photosynthetic capacity of individual leaves decreased little until the deepest stage of true dormancy, as compared with the stage of vegetative growth. While, photosynthetic capacity of intact plants at and after the deepest stage of true dormancy decreased to one third or lower of that at the vegetative stage. This decrease was almost parallel with that of total leaf area. The contribution rate of each of the 3 upper unfolded leaves, except the uppermost one, was 20-25% and higher than the rates of the lower leaves.2. When plants were kept for 15h in a glasshouse without heating after being fed with 14CO2, respiratory loss of assimilated 14C decreased gradually from 70-54% at the stage of vegetative growth to 31% at the stage of imposed dormancy. Also, the total accumulation and translocation of 14C into sinks decreased from 21 and 45% at the stage of induction of dormancy to 15 and 22% at the stage of imposed dormancy. When plants were kept at 18°C after feeding, the values of such parameters changed little with the time of feeding.3. The distribution pattern of 14C was affected little by the temperature during translocation, and seemed to be influenced mainly by the relative strength of sinks. Thus the percentage distribution to young leaves was high during vegetative growth and decreased towards the stage of imposed dormancy, while the percentage distribution to the roots changed inversely to that at the vegetative stage. In bearing plants, however, flower clusters behaved as stronger sinks than roots.4. Amounts of 14C accumulated in the respective sinks were influenced mainly by the total 14C assimilated by the source leaf, rather than by the percentages accumulated or distributed to the sinks. Thus 14C was accumulated in large quantities in the respective sinks from the stage of vegetative growth through induction of dormancy, when 14C accumulated in the leaves exceeded that in the roots, reaching about half of 14C assimilated. But at and after the deepest stage of true dormancy, when total accumulation decreased, 14C accumulated in the leaves decreased markedly, while nearly half of the total was still distributed to the roots.

Pathway of Photosynthate Transfer in the Developing Seed ofVicia fabaL. Transfer in Relation to Seed Anatomy

The seed coat vascular system of the developing seed of Vicia faba consists of a chalazal and two lateral veins. The veins are embedded in parenchymatous tissue which lies beneath the hypodermis and is divided into chlorenchyma, ground parenchyma and thin-walled parenchyma. The thin-walled parenchyma cells and, in old seed coats, the vascular parenchyma of the veins undergo additional secondary wall development to form transfer cells. Thus, transfer cells line the entire inner surface of the seed coat. Initial distribution of 14C-photosynthates and sodium fluorescein within the seed coat was in the vascular system. Subsequent transfer towards the embryo was either radially through vascular parenchyma and thin-walled parenchyma to thin-walled parenchyma/transfer cells, or by lateral spread within the ground and thin-walled parenchyma/transfer cells of the non-vascular region of the seed coat prior to radial transfer. One-third of the 14C-photosynthate delivered to the enclosed embryo was estimated to be transferred via the non-vascular region of the seed coat. The cotyledons consist of a single-layered epidermis enclosing storage parenchyma in which a differentiating reticulate vascular system is embedded. Epidermal cells juxtaposed to the seed coat develop wall ingrowths characteristic of transfer cells. Initial distribution of 14C-photosynthate within the cotyledons reflected the unequal delivery to the seed apoplast from the vascular and non-vascular regions of the seed coat. Subsequent even distribution of photosynthate within the cotyledons possibly occurred by transfer within their vascular system.

Photosynthate Partitioning in Alfalfa Before Harvest and During Regrowth

During the harvest regrowth cycle of alfalfa (Medicago sativa L.) plants, factors such as source to sink distance, sink size, and interorgan competition continually change. However, consequent changes in the pattern of photosynthate partitioning from leaves to other organs are poorly understood. Our objective was to examine photosynthate partitioning from upper and lower alfalfa leaves at intervals before herbage harvest and during regrowth after harvest. The uppermost or lowest fully expanded leaf on the longest or dominant stem was labeled with 14CO2. After a 24‐h translocation period, the plants were divided into various organs to determine distribution of the radiocarbon. Partitioning from upper and lower source leaves was similar before harvest and during the first 9 d of vegetative regrowth after harvest. During regrowth, photosynthate partitioning to the rapidly growing meristematic regions of the dominant stem progressively increased by three to fivefold at the expense of the crown shoots, crown, root, and nodules. At Day 21 following harvest, differences in the distribution of photosynthate from the leaf positions were pronounced. At that time, the upper leaf preferentially partitioned photosynthate to the shoot apex, unexpanded leaves and axillary shoots of the dominant shoot, whereas the lower leaf preferentially distributed photosynthate to the crown shoots, crown, root, and nodules. Expressions of 14C partitioning were affected differently by organ mass. While the smallest organs such as nodules and unexpanded leaves always ranked higher for 14C based on relative specific activity, the largest organs such as roots and crown shoots accumulated the largest percentage of total plant recovered radioactivity. The results illustrate the importance of growth stage and leaf position in photosynthate partitioning in alfalfa and the dominance of herbage meristems for current photosynthate during regrowth.

Photosynthate allocation in loblolly pine (Pinustaedd) seedlings as affected by moisture stress

The effects of recent water stress on distribution of 14C-labelled photosynthate in loblolly pine (Pinustaeda L.) seedlings were examined. Leaves on a lateral branch were allowed to photosynthetically fix 14C, and 14C levels in seven biochemical fractions in the source leaves and in each of five other plant parts were determined 72 h later. Regardless of stress level, about 95% of the 14C originally presented was taken up and 60% was respired during the 72 h translocation period. Most 14C was found in exposed or source leaves and in the roots, with very little occurring above the level of the exposed branch. The bud and nonexposed leaves contained 1.2% or less of the seedling's 14C. As preexposure stress level increased, translocation to roots and other sinks decreased. Sugars contained most of the 14C in parts other than the bud and nonexposed leaves. The proportion of 14C in sugars in these parts increased as stress increased. Structural compounds contained less 14C as stress increased, indicating a lasting effect of stress on growth. In all cases, organic acids and amino acids contained very little 14C. Mild stress resulted in increased starch production in the source leaves relative to no stress, while severe stress reduced starch production.

Kentucky Bluegrass Photosynthate Partitioning Following Scheduled Mowing

Abstract The distribution of photosynthetically fixed carbon within a turfgrass sod was investigated following a routine mowing. The partitioning of 14C-labeled photosynthate was monitored in Kentucky bluegrass (Poa pratensis L. cvs. Baron and Merion) turf 2, 24, and 72 hr after mowing at 3.8 cm. Circles of turf (15 cm in diameter) were exposed to 14CO2 for 15 min, 10-cm-diameter plugs were removed 2 and 24 hr after exposure, and the plants were assayed for radioactivity. Experiments were conducted in late spring, midsummer, and early autumn for 2 years in field plots on a silt loam. Photosynthate translocation from leaf blades to leaf sheaths and crowns was reduced by as much as 25% within 2 hr after mowing but generally returned to a constant and greater rate within 24 hr. Midsummer mowing temporarily inhibited photosynthate transport more than mowing in spring or fall. Photosynthate distribution within turfgrass plants was influenced more by time of year and nutritional status than by mowing. Kentucky bluegrass maintained as closely mowed turf sustains only a slight and temporary disturbance in energy partitioning in response to mowing.

Photosynthate distribution by microplankton in permanently ice‐covered Antarctic desert lakes1

The distribution of 14C‐labeled photosynthate by microplankton in Lakes Vanda and Fryxell, Antarctica, was measured during the 1984–1985 austral summer. Both lakes had conspicuous deep chlorophyll maxima near the bottom of the oxygenated zone. DCMU sensitivity experiments revealed that photosynthesis below the chlorophyll maximum in Lake Fryxell was partially due to photosynthetic bacteria. These bacteria had notably higher protein and lower lipid labeling than overlying oxic microalgae. Protein labeling in the oxic microalgae had lower Ik and higher α values than for other photosynthetic end products, indicating that protein is synthesized more efficiently at low photosynthetic photon flux density than the other metabolites. The Ik values for complete photosynthesis (<20 µEinst m−2 s−1) are among the lowest yet recorded for phytoplankton.

Effect of mecoprop on plant growth and distribution of photosynthate in wheat (Triticum aestivum L.) seedlings

Summary: Résumé: ZusammenfassungFoliar application of the phenoxy‐acid herbicide, mecoprop, at four times normal field rate, caused decreases in root and shoot growth of wheat (Triticum aestivum L.). The shoot relative growth rate (RGR) was affected before that of the roots but subsequently the root RGR was significantly decreased. The roots of plants affected by mecoprop produced large numbers of short swollen laterals but the root system as a whole gradually recovered. Mecoprop treatment was associated with an immediate and lasting decrease in photo‐synthetic 14CO2 fixation. After a pulse of 14CO2 in the light, the proportion of carbon moving to the roots in treated plants was always decreased but after a 24‐h chase the proportion moving to the roots was initially decreased (2 days after spraying), then increased (9 days after spraying), but later became the same (17 days after spraying) as the water sprayed controls. Possible mechanisms involved with these mecoprop induced changes are discussed. Effets de l'herbicide mécoprop sur le développement végétatif et la répartition de produits photosynthétiques dans des plantules de blé (Triticum aestivum L.)Le mécoprop, acide phénoxypropionique, en application foliaire à quatre fois la dose conseillée, a amené une baisse dans la croissance des racines et des pousses du blé (Triticum aestivum L.). Le taux de croissance relative (RGR) des pousses a témoigné des effets plus tôt que les racines mais ultérieurement le RGR des racines a baissé de façon significative. Les racines des plantes touchées par le mécoprop ont produit de nombreuses ramifications courtes et renflées, mais le système racinaire s'est remis peu à peu. Les traitements au mécoprop sont associés à une baisse immédiate et prolongée dans la fixation du 14CO2 photosynthétique. A la suite d'un marquage au 14CO2à la lumière, la proportion de carbone qui s'acheminait vers les racines des plantes traitées a toujours fait voir une baisse mais au bout d'un intervalle de 24 h, la proportion qui s'acheminait vers les racines a d'abord diminué (2 jours après la pulvérisation) pour augmenter ensuite (9 jours après la pulvérisation). Plus tard (17 jours après la pulvérisation) cette proportion était semblable à celle des témoins ne recevant que de l'eau. Les mécanismea éventuellement enjeu dans ces changements provoqués par le mécoprop sont discutés. Wirkung von Mecoprop auf das Wachstum und die Verteilung von Assimilaten bei Jungpflanzen des Weizens (Triticum aestivum L.)Die Blattapplikation von Mecoprop in der 4 fachen Normaldosierung führte zu einer Abnahme des Wurzel‐und Sprosswachstums des Weizens. Zunächst war das Wachstum des Sprosses, aber später auch das der Wurzeln herabgesetzt. Die Seitenwurzeln waren verkürzt und verdickt, aber nach und nach fand das Wurzelsystem zum normalen Wuchs zurück. Nach der Behandlung nahm die 1414C02‐Assimilation für einige Zeit ab. 9 Tage nach der Behandlung nahm der Transport von Assimilaten in die Wurzeln wieder zu, so dass er 17 Tage nach der Behandlung dieselbe Höhe wie bei den Kontrollpflanzen erreichte. Der mögliche Mechanismus der von Mecoprop herbeigeführten Veränderungen wird diskutiert.

Assimilation and distribution of 14C photosynthate in oilseed rape (Brassica Napus L.)

Labelled carbon dioxide as 14 CO 2 was fed to the terminal raceme and the topmost (flag) leaf of field grown rapeseed plants ( Brassica napus L.) at different stages during reproductive development. Radio-activity in reproductive parts, pedicels and stem material in different sections of the terminal raceme was assessed immediately after labelling. Following feeding of the topmost leaf, plants were harvested after 24 h of 14 C translocation. Reproductive parts in the middle and upper regions of the terminal raceme fixed large amounts of 14 C compared to the basal ones. Carbon assimilated by the flag leaf during mid-late flowering was mainly recovered in the main stem. By comparison, during rapid pod filling 58% of labelled assimilates from this leaf were translocated to the reproductive organs carried by the first primary branch and terminal raceme.

ブドウ‘デラウェア’における光合成産物の転流と分配

Distribution of photosynthates from leaves into different plant parts was studied in potted 2-year-old ‘Delaware’ grape which were exposed to 14CO2 at different stages of berry development. In the first experiment, shoots, trunks, roots, berries and leaves were sampled 6, 24 and 72 hours after 14CO2 feeding and the 14C activities in the ethanol soluble and insoluble fractions were measured. In the second experiment, each ethanol soluble fraction of shoots, berries and leaves being sampled 6 hours after 14CO2 feeding was separated into individual compounds by paper and column chromatography, and the 14C activities were then estimated. The results are summarized as follow1. 14C in the ethanol soluble and insoluble fractions in leaves decreased with time after 14CO2 feeding. The 14C labelled photosynthates translocated from leaves into shoots, trunks and roots increased in the ethanol insoluble fraction 24 and 72 hours after feeding, but did not increase in the ethanol soluble fraction.2. The amount of 14C translocated into berries increased at Stage I and III, and appeared mostly in the ethanol soluble fraction in both stages.3. In seeds, more 14C was found in the ethanol insoluble fraction than in the ethanol soluble fraction, and the incorporation ratio increased in the course of berry development from Stage I to Stage II.4. In leaves and shoots, the 14C incorporated into the sugar fraction was mainly found in sucrose, glucose and fructose, and that in the organic acid fraction was mainly in malic acid and tartaric acid. In berries, the distribution of 14C into sugar and organic acid fractions was similar to that in leaves and shoots, except for sucrose. However, the 14C distribution ratio varied at different stages of berry development.

Response of pearl millet to light and temperature

Temperature exerts a major effect on the rate at which crop plants develop and on processes of expansion and extension. Light determines the rate of growth (i.e., dry-matter production) at any stage of development. But three are important interactions: development can be slowed by low light and growth can be retarded when the temperature is too high or too low. The simplest development response is that of germination when light is not a factor. Germination rate of pearl millet cv. BK 560 increased linearly with temperature from a base of 10–12°C to a sharply defined optimum at 33–34°C and declined to zero at about 45–47°C. Other developmental processes such as leaf and spikelet initiation and tillering responded similarly to temperature. The limited information available suggests that the base temperature at which development stops is different for contaasting varieties: the rate and the duration of specific developmental processes also differ. Rate of leaf extention is also a linear function of temperature up to about 34°C so that the time needed to form a complete canopy decreases with increasing temperature below that limit. However, the amount of dry matter produced per unit of intercepted radiation appears to be conservative at about 2.4 g/MJ (+10%) for mean air temperatures ranging from 20 to 36°C. The highest yield, both biological and economic, was obtained at 22°C, mainly because the duration of cv. BK 560 was about 30 days longer at 22 than at 31°C, for example. The effects of temperature on the distribution of photosynthate and nitrate and nitrogen uptake in other cultivate of pearl millet are also discussed. Priorities for research are summarised in the Conclusion.